CHARACTERISTICS OF THE FORTNIGHTLY SHELF WAVE ALONG THE GHANA COAST.

Data from the Ghana shelf has been analyzed to elucidate further the properties of the fortnightly wave that has been observed propagating westward along the Gulf of Guinea coast. Harmonic analysis reveals a highly coherent signal with a large quality factor Q and signal to noise ratio at the luni-solar synodic M//sf fortnightly tidal frequency. The energy is trapped below the thermocline, suggestive of a topographic shelf wave. The wave is not confined to the coastal upwelling season but is manifest in the surface temperature only when the thermocline rises to the surface. Since the Rossby radius of deformation is greater than the shelf width, the model of a hybrid topographic shelf wave modified by stratification is probably the most appropriate.